Preprints
https://doi.org/10.5194/acp-2020-114
https://doi.org/10.5194/acp-2020-114

  25 Feb 2020

25 Feb 2020

Review status: a revised version of this preprint is currently under review for the journal ACP.

The consistency between observations (TCCON, surface measurements and satellites) and CO2 models in reproducing global CO2 growth rate

Lev D. Labzovskii1, Samuel Takele Kenea1, Jinwon Kim1, Haeyoung Lee2, Shanlan Li1, Young-Hwa Byun1, Tae-Young Goo1, and Young-Suk Oh1 Lev D. Labzovskii et al.
  • 1Climate Research Division, National Institute of Meteorological Sciences, Seogwipo, Jeju, 63568, Republic of Korea
  • 2Environmental Meteorology Research Division, National Institute of Meteorological Sciences, Seogwipo, Jeju, 63568, Republic of Korea

Abstract. Atmospheric CO2 growth is the primary driver of the global warming and the rate of this growth is a valuable indicator of the interannual changes in carbon cycle. Despite atmospheric CO2 growth rate had been considered as the well-known quantity, the latest findings indicated that CO2 models can considerably disagree in reproducing this rate. This study is aimed to advance our knowledge about temporal and spatial variations of annual CO2 growth rate (AGR) by using CO2 observations from the Total Column Observing Network (TCCON), CO2 simulations from Carbon Tracker (CT) and Copernicus Atmospheric Monitoring System (CAMS) models being compared with the previously-reported global references of AGR from Global Carbon Budget (GCB) and satellite observations (SAT) for 2004–2019 years. TCCON and the CO2 models revealed temporal AGR variations (AGRTCCON = 1.71–3.35 ppm, AGRCT = 1.64–3.15 ppm, AGRCAMS = 1.66–3.13 ppm) of very similar magnitude to the global CO2 growth references (AGRGCB = 1.59–3.23 ppm, AGRSAT = 1.55–2.92 ppm). However, AGRTCCON estimates agree well with the references only during the 2010s (correlation coefficient, r = 0.68 vs GCB and r = 0.75 vs SAT) as the TCCON observational coverage has been substantially expanded since 2009. Moreover, AGRTCCON reasonably agrees (r = 0.67) with the strength of El-Nino Southern Oscillations (ENSO) in the 2010s. The highest atmospheric CO2 growth (2015–2016) driven by the very strong El-Nino was accurately reproduced by TCCON which provided AGR of 2015–2016 years (3.29 ± 0.98 ppm) in very close agreement to the AGRSAT reference (3.23 ± 0.50 ppm). We further validated AGR simulations (CT and CAMS) versus the newly-acquired AGRTCCON (as point-location reference) for every TCCON site and found low agreement between the models and TCCON (r < 0.50) only at 3 out of 20 stations. This minor caveat has not affected the accuracy of global AGR simulations as they showed high agreement with SAT (r ≈ 0.76–0.78) and GCB (r ≈ 0.72–0.78) and reasonable agreement with TCCON (r = 0.65) global-scale references. The spatial correlation between CT and CAMS in simulating AGR (applied for every 3°×2° grid cell) is perfect (r = 0.99) for the modeling period (2004–2016). Similarly, land-wise intercomparison between CAMS and CT simulations of AGR yielded in perfect correlation for most MODIS land classes (median of land-dependent r > 0.98). From spatial perspective, the highest AGR estimates (> 20 % from the median) were observed in the regions of intense fossil fuel combustion (East Asia) or biomass burning (Amazon, Central Africa). Lack of ideal correlation and small disagreement between CT and CAMS (< 3.9 % difference between medians of global AGR estimates) are likely driven by the slight spatial disagreement between CT and CAMS in the aforementioned regions. To validate this statement, a sensitivity experiment is needed where in CO2 inverse model, alongside with the current setup of a priori biomass burning fluxes, an alternative setup is assembled (multiple independent estimates of burned area and fire-dependent emission factors for various type of tropical fires can be used). In overall, our study showed that the current estimates of global atmospheric growth rate of CO2 are consistent across a wide range of the different data sources and strengthening of carbon observational infrastructure (like covering more developing countries with ground-based CO2 observations and providing more satellite CO2 observations from cloudy and hazy regions) should improve the accuracy of CO2 growth rate estimates on both local and global scales.

Lev D. Labzovskii et al.

 
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Lev D. Labzovskii et al.

Lev D. Labzovskii et al.

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Short summary
Global CO2 growth rate is a key indicator of the balance between carbon sources and sinks but there are few observational methods to quantify this rate. We proved that the estimates of global CO2 growth rate are consistent across wide range of data sources. This finding is essential given recently shown disagreement between CO2 models in simulating global CO2 growth rate, lack of consensus about the method for quantifying this rate and dearth of observational methods to infer global CO2 growth.
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